Quartz OSL dating of lake shoreline ridge sediments:A case study of Lake Xingkai, Northeast China

Abstract

古湖岸堤是湖面波动的地貌证据,可以用来重建古湖泊演化.古湖岸堤沉积物的准确测年是应用此地貌学证据重建湖泊演化的关键.以我国兴凯湖最低一级湖岸堤——大湖岗为研究对象,采用石英小片技术,应用单片再生剂量法(SAR)对大湖岗2个不同位置的剖面风成砂质沉积物(共13个样品)进行了光释光(OSL)测年.样品石英组分的光释光衰减曲线特征表明,样品的释光信号以快组分为主,预热坪和实验室剂量恢复实验结果表明,SAR法可以用来测量兴凯湖古湖岸堤样品的等效剂量.通过分析样品等效剂量分布情况和比较3种年龄模型(平均值模型、中值模型和最小值模型),认为大湖岗湖滨砂质沉积物在沉积埋藏前石英光释光信号晒退完全,获得的OSL年龄是可信的.年代结果表明,大湖岗采自不同位置的2个剖面的年代范围一致,且各个剖面中所有年代均随地层顺序变化;另外,2个样品的OSL年龄与同层位的炭屑样品的¹⁴C年代结果在误差范围内一致,进一步表明OSL测年技术可以获得可靠的兴凯湖岸堤沉积物的年龄.尽管与前人使用热释光(TL)测年方法研究大湖岗形成年代有较大差别,本文认为兴凯湖最低一级古湖岸堤——大湖岗形成于距今约1.24-0.50 ka.;Positions of lake shoreline ridges are indicative of the fluctuations in lake level and can be used for reconstruction of palaeolake evolution history. Reliable and accurate chronology is necessary for using lake shoreline ridge sediments to infer lake geomorphologic variations. This paper selected the Dahugang (DHG) shoreline ridge of Lake Xingkai (Northeast China) to demonstrate the potential of optically stimulated luminescence (OSL) dating technique in sandy shoreline sediments. Thirteen sedimentary samples were collected from two profiles (DHG1 and DHG2) of DHG shoreline ridge. Using single-aliquot regenerative dose (SAR) procedure, equivalent dose (D_e) of all samples was measured in small aliquot. The OSL signals of our samples decay very quickly, indicating that the OSL signal is dominated by fast component; preheat plateau tests and dose recovery tests were carried out to select suitable preheat temperature (220℃) for SAR procedure measurement. We analyzed the distributions of D_e for each sample, and compared the D_es derived from three models (Mean age model, Central age model, and Minimum age model). The results suggested that the sandy sediments from DHG shoreline ridge were well bleached prior to deposition and they are appropriate for OSL dating. The resultant OSL ages are stratigraphically ordered at each of the profiles of DHG1 and DHG2, and both have shown that the DHG shoreline was likely to be formed during~1.24-0.50 ka. Furthermore, the robustness and reliability of our OSL ages are validated by two ¹⁴C ages of charcoals. Although our results seem different from previous researches we propose that the DHG shoreline ridge in the Lake Xingkai was formed at around 1.24-0.50 ka based on the present OSL dating results.